1. Field of the Invention
This invention relates to polyamino-bis-maleimide prepolymer, a method for the manufacture thereof, and a method for the manufacture of a laminate using the prepolymer.
2. Description of Prior Art
Heretofore, in the field of heat-resistant laminates which are required to possess high levels of heat resistance, reliability of throughhole connection, dimensional stability, and electric properties, the polyamino-bis-maleimide prepolymer (such as the polyimide prepolymer formed of N,N'-4,4'-diphenylmethane-bis-maleimide and 4,4'-diaminodiphenylmethane disclosed in U.S. Pat. Nos. 3,562,223 and Re 29,316) has been used. This polyamino-bis-maleimide prepolymer has the disadvantage that it is soluble only in special expensive solvents such as N-methyl-2-pyrrolidone (boiling point 202.degree. C. at 760 mmHg) and N,N-dimethylformamide (b.p. 153.degree. C.). From the standpoint of working environment and because of the high ratio of residual solvent in the prepreg, adoption of such a special solvent of high boiling point has not proved advantageous. When such a special solvent of high boiling point is used in the manufacture of a heat-resistant laminated sheet, such properties as boiling water absorption ratio and resistance to measling are adversely affected because the removal of the solvent by drying becomes difficult, the prepreg exudes varnish, and the laminate retains the solvent. To save the situation, the imide type prepolymer which is soluble in a low-boiling point ordinary organic solvent and which is obtained by the reaction of an epoxy compound with bis-imide and diamine has been proposed (U.S. Pat. No. 4,346,206). This imide type prepolymer, however, has the disadvantage that it has a lower glass transition point than the polyamino-bis-imide resin consisting solely of bisimide and diamine because it contains the epoxy compound.
In the circumstance, the desirability of development of a laminate using a polyamino-bis-maleimide resin which permits use of such an inexpensive low-boiling point ordinary solvent as ethyleneglycol monomethyl ether or ethyleneglycol monoethyl ether and which has high heat resistance has found growing recognition.
An object of this invention, therefore, is to provide a polyamino-bis-maleimide prepolymer solution which retains thermal stability, entails no three-dimensional hardening at room temperature, and exhibits excellent curing property during the removal of solvent by drying and acquires outstanding heat resistance after curing and a method for the manufacture of this prepolymer.
Another object of this invention is to provide a prepreg of polyamino-bismaleimide prepolymer which is readily curable. Still another object of this invention is to provide prepreg which permits ready removal of the solvent by drying. Yet another object of this invention is to provide a method for the manufacture of a laminate of polyamino-bis-maleimide resin which acquires outstanding heat resistance after curing.